Broadband ultraviolet illumination sources

ABSTRACT

A broadband ultraviolet illumination source for a characterization system is disclosed. The broadband ultraviolet illumination source includes an enclosure having one or more walls, the enclosure configured to contain a gas, and a plasma discharge device based on a graphene-dielectric-semiconductor (GOS) planar-type structure. The GOS structure includes a silicon substrate having a top surface, a dielectric layer disposed on the top surface of the silicon substrate, and at least one layer of graphene disposed on a top surface of the dielectric layer. A metal contact may be formed on the top surface of the graphene layer. The GOS structure has several advantages for use in an illumination source, such as low operating voltage (below 50 V), planar surface electron emission, and compatibility with standard semiconductor processes. The broadband ultraviolet illumination source further includes electrodes placed inside the enclosure or magnets placed outside the enclosure to increase the current density.

CROSS-REFERENCE

The present application constitutes a divisional application of andclaims priority to U.S. patent application Ser. No. 16/879,310, filed onMay 20, 2020, which is a non-provisional application of U.S. ProvisionalPatent Application No. 62/858,178, filed Jun. 6, 2019, entitledBROADBAND ULTRAVIOLET LIGHT SOURCE, naming Yung-Ho Alex Chuang, YinyingXiao-Li, Edgardo Garcia-Berrios, and John Fielden as inventors, which isincorporated herein by reference in the entirety.

TECHNICAL FIELD

The present disclosure relates generally to characterization systems,and more particularly, to broadband ultraviolet (UV) illuminationsources for use in characterization systems.

BACKGROUND

The integrated circuit (IC) industry requires inspection tools withincreasingly higher sensitivity to detect ever smaller defects andparticles whose sizes may be a few tens of nanometers (nm), or less.These inspection tools must operate at high speed in order to inspect alarge fraction, or even 100%, of the area of a sample, in a short periodof time. For example, inspection time may be approximately one hour forinspection during production or, at most, a few hours for research anddevelopment or troubleshooting. In order to inspect quickly, inspectiontools use pixel or spot sizes larger than the dimensions of the defector particle of interest, and detect just a small change in signal causedby a defect or particle. Detecting a small change in signal requires ahigh light level and a low noise level. High speed inspection is mostcommonly performed in production using inspection tools operating withUV light. Inspection in research and development may be performed withUV light or with electrons.

The IC industry also requires high precision metrology tools foraccurately measuring the dimensions of small features down to a fewnanometers or less on samples. Metrology processes are performed onsamples at various points in a semiconductor manufacturing process tomeasure a variety of characteristics of the samples such as a width of apatterned structure on the sample, a thickness of a film formed on thesample, and overlay of patterned structures on one layer of the samplewith respect to patterned structures on another layer of the sample.These measurements are used to facilitate process controls and/or yieldefficiencies in the manufacturing of semiconductor dies. Metrology maybe performed with UV light or with electrons.

The semiconductor industry, which is aimed at producing integratedcircuits with higher integration, lower power consumption and lowercosts, is one of the main drivers of UV optics. The development ofpowerful UV light sources such as the excimer lasers andfrequency-multiplied solid-state lasers has led to the growth ofresearch and development efforts in the field of UV photon applications.However, conventional UV light sources have a limited amount of emissionin the deep UV range. Further, with conventional UV light sourcesdischarge rapidly degrades, which limits the lifetime of the UV lightsource.

Therefore, it would be desirable to provide a system and method thatcures the shortfalls of the previous approaches identified above.

SUMMARY

A characterization system is disclosed, in accordance with one or moreembodiments of the present disclosure. In one embodiment, the systemincludes a stage assembly configured to support a sample. In anotherembodiment, the system includes a broadband ultraviolet illuminationsource. In another embodiment, the broadband ultraviolet illuminationsource includes an enclosure having one or more walls, the enclosureconfigured to contain a gas. In another embodiment, the broadbandultraviolet illumination source includes a plasma discharge device. Inanother embodiment, the plasma discharge device includes an anode. Inanother embodiment, the plasma discharge device includes a cathode. Inanother embodiment, the cathode includes a silicon substrate including atop surface. In another embodiment, the cathode includes a dielectriclayer disposed on the top surface of the silicon substrate. In anotherembodiment, the cathode includes at least one layer of graphene formedon a top surface of the dielectric layer. In another embodiment, thecathode includes a metal contact formed on a top surface of the graphenelayer. In another embodiment, the cathode includes a second power supplysource configured to apply a voltage between the metal contact and thesilicon substrate. In another embodiment, the plasma discharge deviceincludes a first power supply source configured to apply a voltagebetween the anode and the cathode. In another embodiment, the systemincludes one or more optical elements configured to direct illuminationfrom the broadband ultraviolet illumination source to the sample. Inanother embodiment, the one or more optical elements are configured todirect illumination reflected from the sample to a sensor.

A broadband illumination source is disclosed, in accordance with one ormore embodiments of the present disclosure. In one embodiment, theillumination source includes an enclosure having one or more walls, theenclosure configured to contain a gas. In another embodiment, theillumination source includes a plasma discharge device. In anotherembodiment, the plasma discharge device includes an anode. In anotherembodiment, the plasma discharge device includes a cathode. In anotherembodiment, the plasma discharge device includes at least one of a focuselectrode and magnet configured to focus electrons emitted by thecathode to increase the plasma density. In another embodiment, thecathode includes a silicon substrate including a top surface. In anotherembodiment, the cathode includes a dielectric layer disposed on the topsurface of the silicon substrate. In another embodiment, the cathodeincludes at least one layer of graphene formed on a top surface of thedielectric layer. In another embodiment, the cathode includes a metalcontact formed on a top surface of the graphene layer. In anotherembodiment, the cathode includes a second power supply source configuredto apply a voltage between the metal contact and the silicon substrate.In another embodiment, the plasma discharge device includes a firstpower supply source configured to apply a voltage between the anode andthe cathode.

A method for exposing a substrate to broadband ultraviolet radiation isdisclosed, in accordance with one or more embodiments of the presentdisclosure. In one embodiment, the method includes: supplying a gas toan enclosure of a broadband illumination source; generating a plasmainside the enclosure using a plasma discharge device; generatingbroadband ultraviolet radiation in the enclosure; and optically couplingthe broadband ultraviolet radiation to a substrate located outside theenclosure. In another embodiment, the plasma discharge device includesan anode. In another embodiment, the plasma discharge device includes acathode. In another embodiment, the cathode includes a silicon substrateincluding a top surface. In another embodiment, the cathode includes adielectric layer disposed on the top surface of the silicon substrate.In another embodiment, the cathode includes at least one layer ofgraphene formed on a top surface of the dielectric layer. In anotherembodiment, the cathode includes a metal contact formed on a top surfaceof the graphene layer. In another embodiment, the cathode includes asecond power supply source configured to apply a voltage between themetal contact and the silicon substrate. In another embodiment, theplasma discharge device includes a first power supply source configuredto apply a voltage between the anode and the cathode.

It is to be understood that both the foregoing general description andthe following detailed description are exemplary and explanatory onlyand are not necessarily restrictive of the invention as claimed. Theaccompanying drawings, which are incorporated in and constitute a partof the specification, illustrate embodiments of the invention andtogether with the general description, serve to explain the principlesof the invention.

BRIEF DESCRIPTION OF DRAWINGS

The numerous advantages of the disclosure may be better understood bythose skilled in the art by reference to the accompanying figures inwhich:

FIG. 1 illustrates a simplified schematic view of a characterizationsystem, in accordance with one or more embodiments of the presentdisclosure;

FIG. 2A illustrates a schematic diagram of a broadband ultravioletillumination source, in accordance with one or more embodiments of thepresent disclosure.

FIG. 2B illustrates a schematic diagram of a broadband ultravioletillumination source, in accordance with one or more embodiments of thepresent disclosure.

FIG. 3 illustrates a cross-sectional side view of a knowngraphene-dielectric-semiconductor of the broadband ultravioletillumination source, in accordance with one or more embodiments of thepresent disclosure; and

FIG. 4 is a flow diagram depicting a method for exposing a substrate tobroadband ultraviolet radiation, in accordance with one or moreembodiments of the present disclosure.

DETAILED DESCRIPTION

The present disclosure has been particularly shown and described withrespect to certain embodiments and specific features thereof. Theembodiments set forth herein are taken to be illustrative rather thanlimiting. It should be readily apparent to those of ordinary skill inthe art that various changes and modifications in form and detail may bemade without departing from the spirit and scope of the disclosure.

Reference will now be made in detail to the subject matter disclosed,which is illustrated in the accompanying drawings.

Broadband ultraviolet illumination sources are used for variousapplications in the semiconductor processing industry. It is desirablefor the illumination source to have a long useful lifetime, highbrightness, and a broad spectral range of emitted illumination.Currently, plasma-based illumination sources are used in semiconductorcharacterization systems. Plasma-based illumination sources generallyinclude an enclosure containing a cathode, an anode, and a discharge gas(e.g., argon, xenon, deuterium, mercury vapor, or a combination ofsuch). A voltage between the cathode and anode maintains a plasma orelectric arc.

The most common commercially available vacuum ultraviolet (VUV)illumination source is a low-pressure deuterium discharge lamp, whichuses a tungsten filament and anode placed on opposite sides to producethe output spectrum. Unlike an incandescent bulb, the tungsten filamentis not the source of illumination in deuterium lamps. Instead, adischarge is created from the filament to the anode. Deuterium lampsexhibit a relatively high radiant output at wavelengths from about 120nm to about 160 nm but a relatively low radiant output at wavelengthsgreater than about 170 nm. Since for many applications it is desirableto use broadband radiation that spans vacuum ultraviolet, ultraviolet,visible and near infrared ranges, for those applications it is currentlynecessary to combine the output of a deuterium lamp with the output fromanother lamp, such as a xenon arc lamp or quartz-halogen lamp to coverthe whole wavelength range.

Conventional plasma illumination sources suffer from a number ofdrawbacks when used in semiconductor characterization systems. The firstdrawback is that plasma illumination sources based on mercury, argon,xenon, or a combination of such have a limited amount of emission in thedeep UV range. It would be desirable to increase the amount of emissionat vacuum wavelengths below approximately 200 nm. Even thoughcommercially available deuterium discharge lamps can emit at VUVwavelengths, there is still a drawback that is particularly relevant tosemiconductor characterization systems. For example, the discharge tendsto rapidly degrade. As the source ages, the cathode tends to erodeand/or become contaminated and the arc tends to spread. Tungsten comingfrom the filaments in the deuterium lamps can contaminate the lampenclosure and the output window. This limits the lifetime of thedeuterium discharge lamps. The typical lifetime of a deuterium lamp isapproximately 2000 hours. In addition, deuterium discharge lamps operateat high voltages. The firing voltages are about 300 to 500 volts. Oncethe discharge starts, the voltage drops to around 100 to 200 volts.

Embodiments of the present disclosure are directed to a broadband UVillumination source for use in semiconductor characterization systems.More particularly, embodiments of the present disclosure are directed toa broadband UV illumination source including, but not limited to, agraphene electron emitter as an electron discharge source, an anode, andan enclosure having one or more transparent walls. In this embodiment,the enclosure contains a gas, wherein the gas contained within theenclosure may include, but is not limited to, at least one of hydrogen,deuterium, or a noble gas. Specifically, the electron discharge sourceincludes a graphene-dielectric-semiconductor (also referred to as agraphene-oxide-semiconductor (GOS)) type structure. The GOS structureincludes a silicon substrate having a top surface; a dielectric layerdisposed on the top surface of the silicon substrate, and at least onelayer of graphene disposed on the top surface of the dielectric layer.Metal contacts may be formed on top of the graphene.

It is noted herein that for purposes of the present disclosure, theterms “graphene-oxide-semiconductor,” “GOS,”“graphene-dielectric-semiconductor,” and variants thereof may be usedinterchangeably throughout and may be considered equivalent for purposesof the present disclosure, unless noted otherwise herein. GOS structuresare generally discussed in K. Murakami, S. Tanaka, A. Miyashita, M.Nagao, Y. Nemoto, M. Takeguchi, and J. Fujita,“Graphene-oxide-semiconductor planar-type electron emission device,”Appl. Phys. Lett. 108, 083506 (2016); and K. Murakami, T. Igari, K.Mitsuishi, M. Nagao, M. Sasaki, and Y. Yamada, “Highly MonochromaticElectron Emission from Graphene/Hexagonal Boron Nitride/SiHeterostructure,” ACS Appl. Materials & Interfaces 12, 4061-4067 (2020),which are each herein incorporated by reference in the entirety.

This GOS structure has several advantages such as low operating voltage(below 50 V), planar surface electron emission, and compatibility withstandard semiconductor processes. Graphene is a single layer of carbonatoms arranged in a hexagonal lattice exhibiting high electricalconductivity. In addition, the electron scattering cross section ofcarbon atoms is smaller than that of conventional metal electrodes suchas gold and aluminum. Therefore, the use of graphene as the topmost gateelectrode may allow electron emission efficiency to reach 20% to 30% ifthe graphene layer is grown with low-pressure chemical vapor deposition(LPCVD). See, for example, K. Murakami, J. Miyaji, R. Furuya, M. Adachi,M. Nagao, Y. Neo, Y. Takao, Y. Yamada, M. Sasaki, H. Mimura,“High-performance planar-type electron source based on agraphene-oxide-semiconductor structure,” Appl. Phys. Lett. 114, 213501(2019), which is herein incorporated by reference in the entirety. Theelectron emission efficiency may be further improved if only a fewlayers of graphene (ideally a single graphene layer) are used in the GOSstructure. Owing to low temperature operation, unlike tungstenfilaments, little graphene may be evaporated or sputtered and so may notcontaminate the broadband UV source. The energy spread of the GOSstructure may be less than about 1.5 eV.

An additional embodiment of the present disclosure is directed to abroadband illumination source including a plasma discharge deviceconfigured to maintain a plasma discharge in a gas contained with anenclosure of the broadband illumination source. The plasma dischargedevice includes electrodes inside the enclosure, and one or more magnetsplaced outside the enclosure to increase the current density as in anelectron focusing system. Electron trajectories will tend to followspiral paths spiraling around magnetic field lines. The one or moremagnets (e.g., permanent magnets or electromagnets) placed outside theenclosure provide a magnetic field to confine the plasma discharge intoa small volume within the enclosure. The one or more magnets areconfigured to increase the magnetic field strength near the anoderelative to the magnetic field strength at the electron dischargesource, so as to reduce the width of the discharge plasma and increasethe plasma density close to the anode.

Another embodiment of the present disclosure is directed to acharacterization system. More particularly, embodiments of the presentdisclosure are directed to a characterization system including abroadband ultraviolet discharge lamp using a GOS structure as theelectron discharge source, an anode, and an enclosure having one or moretransparent walls. The broadband illumination source may further includea plasma discharge device configured to maintain a plasma discharge ofthe gas within the enclosure. Additionally, the broadband illuminationsource may include one or more magnets configured to increase the plasmadensity close to the anode. Further, a substrate support may be locatedoutside the discharge lamp. The broadband illumination source mayfurther include one or more optic elements configured to be adapted tocouple radiation from the discharge lamp to a substrate located on thesubstrate support.

Another embodiment of the present disclosure is directed to a method forexposing a substrate to broadband ultraviolet radiation. A gascontaining at least one of hydrogen, deuterium and a noble gas issupplied to an enclosure, and a plasma is generated inside the enclosurewith the gas using a GOS structure and an anode. The method may furtherinclude increasing the plasma density close to the anode by placingmagnets outside the enclosure. Radiation generated as a result of theplasma discharge may be optically coupled to a substrate located outsidethe enclosure.

FIG. 1 illustrates a simplified schematic view of a characterizationsystem 100, in accordance with one or more embodiments of the presentdisclosure. For example, the characterization tool 100 may include, butis not limited to, an inspection sub-system or a metrology sub-systemconfigured to inspect or measure a sample 108. Sample 108 may includeany sample known in the art such as, but not limited to, a wafer,reticle, photomask, or the like.

The characterization system 100 may include any characterization systemknown in the art including, but not limited to, an optical-basedinspection tool, a review tool, an image-based metrology tool, and thelike.

In one embodiment, the sample 108 is disposed on a stage assembly 112 tofacilitate movement of the sample 108. The stage assembly 112 mayinclude any stage assembly known in the art including, but not limitedto, an X-Y stage, an R-θ stage, and the like. In another embodiment, thestage assembly 112 is capable of adjusting the height of the sample 108during inspection to maintain focus on the sample 108.

In another embodiment, the characterization system 100 includes anillumination source 102 configured to generate an illumination beam 101.The illumination source 102 may include any illumination source known inthe art suitable for generating an illumination beam 101. For example,the illumination source 102 may emit near infrared (NIR) radiation,visible radiation, ultraviolet (UV) radiation, near UV (NUV), deep UV(DUV) radiation, vacuum UV (VUV) radiation, and the like. For instance,the illumination source 102 may include one or more lasers. In anotherinstance, the illumination source 102 may include a broadbandillumination source.

In another embodiment, the characterization system 100 includes anillumination arm 107 configured to direct illumination from theillumination source 102 to the sample 108. The illumination arm 107 mayinclude any number and type of optical components known in the art. Inone embodiment, the illumination arm 107 includes one or more opticalelements 103. In this regard, illumination arm 107 may be configured tofocus illumination from the illumination source 102 onto the surface ofthe sample 108. It is noted herein that the one or more optical elements103 may include any optical element know in the art including, but notlimited to, an objective lens 105, one or mirrors, one or more lenses,one or more polarizers, one or more beam splitters, or the like.

In another embodiment, a collection arm 109 is configured to collectillumination reflected, scattered, diffracted, and/or emitted from thesample 108. In another embodiment, the collection arm 109 may directand/or focus the illumination from the sample 108 to a sensor 106 of adetector assembly 104. It is noted herein that sensor 106 and thedetector assembly 104 may include any sensor and detector assembly knownin the art. The sensor may include, but is not limited to,charge-coupled device (CCD detector), a complementary metal oxidesemiconductor (CMOS) detector, a time-delay integration (TDI) detector,a photomultiplier tube (PMT), an avalanche photodiode (APD), a linesensor, an electron-bombarded line sensor, or the like.

In another embodiment, the detector assembly 104 is communicativelycoupled to a controller 114 including one or more processors 116 andmemory 118. For example, the one or more processors 116 may becommunicatively coupled to memory 118, wherein the one or moreprocessors are configured to execute a set of program instructionsstored on memory 118. In one embodiment, the controller 114 controls thecharacterization system 100 and/or the sensor 106 to characterize (e.g.,inspect or measure) a structure on sample 108.

In one embodiment, illumination source 102 includes a broadband UVillumination source including a graphene-dielectric-semiconductor (GOS)structure. The broadband UV illumination source may include, but is notlimited to, an electron discharge source, an anode, an enclosure havingone or more transparent walls, and the like. The enclosure may include agas. For example, the gas contained within the enclosure may include,but is not limited to, hydrogen, deuterium, and/or a noble gas such as,but not limited to, helium, neon, argon, krypton, or xenon.

In one embodiment, the broadband ultraviolet source includes a plasmadischarge device configured to maintain a plasma discharge of the gaswithin the enclosure. The illumination beam 101 of the illuminationsource 102 may include wavelengths in an ultraviolet region, such as ina DUV (˜200 nm to 280 nm) or a VUV (˜100 nm to 200 nm) spectral range.The electron discharge source of the broadband UV illumination sourcemay be based on a GOS-type structure.

In another embodiment, the GOS structure includes agraphene-dielectric-semiconductor planar-type electron emission device.For example, the GOS structure includes, but is not limited to, asilicon substrate having a top surface, a dielectric layer disposed onthe top surface of the silicon substrate, and at least one layer ofgraphene disposed on a top surface of the dielectric layer. Thedielectric layer may include any dielectric known in the art. Forexample, the dielectric layer may include boron nitride or silicondioxide. In another embodiment, metal contacts may be formed on a topsurface of the graphene layer.

In another embodiment, the illumination source 102 includes a broadbandUV illumination source including a GOS structure as the electrondischarge source. In another embodiment, the broadband UV illuminationsource includes an enclosure having one or more transparent walls. Theenclosure may include a gas within the enclosure. For example, the gascontained within the enclosure may include, but is not limited to, atleast one of hydrogen, deuterium, or a noble gas.

In another embodiment, a plasma discharge device is configured tomaintain a plasma discharge of the gas within the enclosure. The outputspectrum (e.g., illumination beam 101) of the illumination source 102may include, but is not required to include, wavelengths in theultraviolet region, such as in a DUV (˜200 nm to 280 nm) or a VUV (˜100nm to 200 nm) spectral range.

In another embodiment, the plasma discharge device includes one or moreelectrodes within the enclosure. In another embodiment, the plasmadischarge device may include one or more magnets placed outside theenclosure. The one or more magnets and/or the one or more electrodes maybe configured to increase the current density as in an electron focusingsystem. It is noted herein that electron trajectories tend to followspiral paths spiraling around magnetic field lines. The one or moremagnets (e.g., permanent magnets or electromagnets) may provide amagnetic field that confines the plasma discharge to a small volumewithin the enclosure. In an example embodiment where an electromagnet isused, a power supply may be configured to apply a DC voltage to theelectromagnet to create a static magnetic field. The one or more magnetsmay be configured to increase the magnetic field strength near the anoderelative to the magnetic field strength at the electron dischargesource, so as to reduce the width of the discharge plasma and increasethe plasma density close to the anode.

In one embodiment, the characterization system 100 illuminates a line onsample 108 and collects scattered and/or reflected illumination in oneor more dark-field and/or bright-field collection channels. In thisembodiment, detector assembly 104 may include a line sensor or anelectron-bombarded line sensor.

In one embodiment, the one or more optical elements 103 includes anillumination tube lens 133. The illumination tube lens 133 may beconfigured to image an illumination pupil aperture 131 to a pupil withinthe objective lens 105. For example, the illumination tube lens 133 maybe configured such that the illumination pupil aperture 131 and thepupil are conjugate to one another. In one embodiment, the illuminationpupil aperture 131 may be configurable by switching different aperturesinto the location of illumination pupil aperture 131. In anotherembodiment, the illumination pupil aperture 131 may be configurable byadjusting a diameter or shape of the opening of the illumination pupilaperture 131. In this regard, the sample 108 may be illuminated bydifferent ranges of angles depending on the characterization (e.g.,measurement or inspection) being performed under control of thecontroller 114.

In one embodiment, the one or more optical elements 103 include acollection tube lens 123. For example, the collection tube lens 123 maybe configured to image the pupil within the objective lens 105 to acollection pupil aperture 121. For instance, the collection tube lens123 may be configured such that the collection pupil aperture 121 andthe pupil within the objective lens 105 are conjugate to one another. Inone embodiment, the collection pupil aperture 121 may be configurable byswitching different apertures into the location of collection pupilaperture 121. In another embodiment, the collection pupil aperture 121may be configurable by adjusting a diameter or shape of the opening ofcollection pupil aperture 121. In this regard, different ranges ofangles of illumination reflected or scattered from the sample 108 may bedirected to detector assembly 104 under control of the controller 114.

In another embodiment, at least one of illumination pupil aperture 131and collection pupil aperture 121 may include a programmable aperture.Programmable apertures are generally discussed in U.S. Pat. No.9,255,887, entitled “2D programmable aperture mechanism,” to Brunner,issued on Feb. 9, 2016; U.S. Pat. No. 9,645,287, entitled “Flexibleoptical aperture mechanisms,” to Brunner, issued on May 9, 2017, both ofwhich are herein incorporated by reference in the entirety. Methods ofselecting an aperture configuration for inspection is generallydescribed in U.S. Pat. No. 9,709,510, entitled “Determining aconfiguration for an optical element positioned in a collection apertureduring wafer inspection,” to Kolchin et al., issued on Jul. 18, 2017;and U.S. Pat. No. 9,726,617, entitled “Apparatus and methods for findinga best aperture and mode to enhance defect detection,” to Kolchin et al,issued on Aug. 8, 2017, both of which are herein incorporated byreference in the entirety.

Characterization systems are generally described in U.S. Pat. No.9,891,177, entitled “TDI Sensor in a Darkfield System”, toVazhaeparambil et al., issued on Feb. 13, 2018; U.S. Pat. No. 9,279,774,entitled “Wafer Inspection”, to Romanovsky et al., issued on Mar. 8,2018; U.S. Pat. No. 7,957,066, entitled “Split Field Inspection SystemUsing Small Catadioptric Objectives,” to Armstrong et al., issued onJun. 7, 2011; U.S. Pat. No. 7,817,260, entitled “Beam Delivery Systemfor Laser Dark-Field Illumination in a Catadioptric Optical System,” toChuang et al., issued on Oct. 19, 2010; U.S. Pat. No. 5,999,310,entitled “Ultra-Broadband UV Microscope Imaging System with Wide RangeZoom Capability,” to Shafer et al., issued on Dec. 7, 1999; U.S. Pat.No. 7,525,649, entitled “Surface Inspection System Using Laser LineIllumination with Two Dimensional Imaging,” to Leong et al., issued onApr. 28, 2009; U.S. Pat. No. 9,080,971, entitled “Metrology Systems andMethods,” to Kandel et al., issued on Jul. 14, 2015; U.S. Pat. No.7,474,461, entitled “Broad Band Objective Having Improved Lateral ColorPerformance,” to Chuang et al., issued on Jan. 6, 2009; U.S. Pat. No.9,470,639, entitled “Optical Metrology With Reduced Sensitivity ToGrating Anomalies,” to Zhuang et al., issued on Oct. 18, 2016; U.S. Pat.No. 9,228,943, entitled “Dynamically Adjustable Semiconductor MetrologySystem,” to Wang et al., issued on Jan. 5, 2016; U.S. Pat. No.5,608,526, entitled “Focused Beam Spectroscopic Ellipsometry Method andSystem,” to Piwonka-Corle et al., issued on Mar. 4, 1997; and U.S. Pat.No. 6,297,880, entitled “Apparatus for Analyzing Multi-Layer Thin FilmStacks on Semiconductors,” to Rosencwaig et al., issued on Oct. 2, 2001,all of which are incorporated herein by reference in the entirety.

It is noted herein that the one or more components of system 100 may becommunicatively coupled to the various other components of system 100 inany manner known in the art. For example, the one or more processors 116may be communicatively coupled to each other and other components via awireline (e.g., copper wire, fiber optic cable, and the like) orwireless connection (e.g., RF coupling, IR coupling, WiMax, Bluetooth,3G, 4G, 4G LTE, 5G, and the like).

The one or more processors 116 may include any one or more processingelements known in the art. In this sense, the one or more processors 116may include any microprocessor-type device configured to executesoftware algorithms and/or instructions. The one or more processors 116may consist of a desktop computer, mainframe computer system,workstation, image computer, parallel processor, or other computersystem (e.g., networked computer) configured to execute a programconfigured to operate the system 100, as described throughout thepresent disclosure. It should be recognized that the steps describedthroughout the present disclosure may be carried out by a singlecomputer system or, alternatively, multiple computer systems.Furthermore, it should be recognized that the steps described throughoutthe present disclosure may be carried out on any one or more of the oneor more processors 116. In general, the term “processor” may be broadlydefined to encompass any device having one or more processing elements,which execute program instructions from memory 118. Moreover, differentsubsystems of the system 100 (e.g., illumination source 102, detectorassembly 104, controller 114, and the like) may include processor orlogic elements suitable for carrying out at least a portion of the stepsdescribed throughout the present disclosure. Therefore, the abovedescription should not be interpreted as a limitation on the presentdisclosure but merely an illustration.

The memory 118 may include any storage medium known in the art suitablefor storing program instructions executable by the associated one ormore processors 116 and the data received from the metrology sub-systemand/or inspection sub-system. For example, the memory 118 may include anon-transitory memory medium. For instance, the memory 118 may include,but is not limited to, a read-only memory (ROM), a random-access memory(RAM), a magnetic or optical memory device (e.g., disk), a magnetictape, a solid-state drive and the like. It is further noted that memory118 may be housed in a common controller housing with the one or moreprocessors 116. In an alternative embodiment, the memory 118 may belocated remotely with respect to the physical location of the processors116, controller 114, and the like. In another embodiment, the memory 118maintains program instructions for causing the one or more processors116 to carry out the various steps described through the presentdisclosure.

FIG. 2A illustrates a schematic diagram of a broadband ultravioletillumination source 200, in accordance with one or more embodiments ofthe present invention. It is noted herein that the description ofvarious embodiments, components, and operations described previouslywith respect to the characterization system 100 should be interpreted toextend to the broadband illumination source 200 unless otherwise notedherein.

In one embodiment, the broadband illumination source 200 includes anenclosure 202 having one or more walls. In another embodiment, the oneor more walls of the enclosure 202 are at least partly transparent. Inthis regard, the one or more walls of enclosure 202 may include amaterial that is transparent or partly transparent at wavelengths ofinterest. For example, the broadband UV illumination source 200 mayinclude, but is not limited to, a transparent window 201 incorporatedinto a wall of the enclosure 202. For instance, at least one of the oneor more walls of the enclosure 202 may be at least partly transparent ata wavelength between 130 nm and 400 nm. The window 201 may be formed ofany material known in the art including, but not limited to, quartz,fused silica, magnesium fluoride (MgF₂), calcium fluoride (CaF₂),strontium tetraborate (SrB₄O₇), or the like.

In one embodiment, a gas 204 is contained within the enclosure 202. Forpurposes of the present disclosure, the term “enclosure” refers to aclosed environment having one or more walls that contain the gas 204,while preventing the ambient atmosphere from undesirably contaminatingthe gas 204. The gas 204 may include, but is not limited to, one or moreof hydrogen, deuterium, or a noble gas. The noble gas may include, butis not limited to, at least one of helium, neon, argon, krypton, xenon,or the like. In one embodiment, the enclosure 202 may be filled with gas204 and then sealed. In another embodiment, an external gas source (notshown) may supply gas 204 as needed to the enclosure 202.

In one embodiment, the broadband ultraviolet illumination source 200 isconfigured to operate as a low-pressure discharge lamp. For example, thebroadband ultraviolet illumination source 200 may operate as alow-pressure discharge lamp with a fill pressure of the gas 204 betweenapproximately 1 Pa and 10000 Pa. In another embodiment, the broadbandultraviolet illumination source 200 is configured to operate as ahigh-pressure discharge lamp. For example, the broadband ultravioletillumination source 200 may operate as a high-pressure discharge lampwith a fill pressure of gas 204 between approximately 10⁴ and 10⁶ Pa(e.g., between approximately 0.1 and 10 atmospheres). It is noted hereinthat the operating pressure of the illumination source 200 may be higherthan the fill pressure depending on the operating temperature of theillumination source 200.

In one embodiment, the enclosure 202 includes a getter 209. For example,the getter 209 may be placed within the enclosure 202 to removeimpurities during operation of the illumination source 200. It is notedherein that the enclosure 202 may include any getter suitable forremoving impurities including, but not limited to, non-evaporablegetters (NEGs), hydrogen getters, evaporable getters, getter films, orthe like.

In one embodiment, the broadband UV illumination source 200 includes aplasma discharge device 207 configured to be adapted to maintain aplasma discharge 208 of the gas 204. For example, the plasma discharge208 of the gas 204 may take place within the enclosure 202. The gaspressure may be between approximately 1 Pa and 10000 Pa for alow-pressure discharge lamp. Further, the gas pressure may be between10⁴ and 10⁶ Pa (e.g., between 0.1 and 10 atm) for a high-pressuredischarge lamp. It is noted herein that the gas pressure may be anypressure suitable to obtain intense radiation of ultravioletillumination from the discharge 208 for use in characterization systems(e.g., the characterization system 100 shown in FIG. 1). In oneembodiment, as shown in FIG. 2A, the plasma discharge device 207includes an anode 210 positioned a select distance from a cathode 212.For example, the anode 210 and cathode 212 may be disposed within theenclosure 202 a select distance apart. In one embodiment, that selectdistance may be approximately equal to 1 mm, such as a distance betweenabout 500 μm and 2 mm.

In one embodiment, the plasma discharge device 207 includes a firstpower supply 214 configured to apply a DC voltage between the anode 210and cathode 212. For example, the voltage may produce an electric fieldthat maintains the discharge 208. In this regard, the discharge 208 mayproduce broadband radiation 216. In another embodiment, the first powersupply 214 applies a voltage between the anode 210 and cathode 212sufficient to ionize a portion of the gas 204 to ignite (or initiate)the discharge 208. For example, a high voltage (e.g., hundreds of Volts)may be applied by the first power supply 214 to ignite the discharge anda lower voltage, (e.g., between approximately 50 V and 200 V) may beapplied to sustain the discharge once ignited. In an alternativeembodiment, the emission current from the cathode 212 may be initiallyincreased to initiate the discharge while maintaining a constant voltageon the anode. As explained below in relation to FIG. 3, the emissioncurrent may be controlled by the bias voltage applied to the GOSstructure.

In one embodiment, the cathode 212 includes a GOS structure including agraphene-dielectric-semiconductor planar-type emission device. Forexample, the GOS structure may include, but is not limited to, a siliconsubstrate having a top surface, a dielectric layer disposed on the topsurface of the silicon substrate, and at least one layer of graphenedisposed on the top surface of the dielectric layer. In someembodiments, metal contacts may be formed on a top surface of thegraphene layer. For purposes of the present disclosure, the term“graphene” refers to a single layer of carbon atoms arranged in ahexagonal lattice exhibiting high electrical conductivity.

It is noted herein that the GOS structure has several advantages such aslow operating voltage (below 50 V), planar surface electron emission,and compatibility with standard semiconductor processes. In addition,the electron scattering cross section of carbon atoms is smaller thanthat of conventional metal electrodes such as gold and aluminum.Therefore, the use of graphene as the topmost gate electrode may allowelectron emission efficiency to reach 20% to 30% if the graphene layeris grown with low-pressure chemical vapor deposition (LPCVD). Unliketungsten filaments, graphene may not be a contaminant for the broadbandUV lamp. The energy spread of electrons emitted from the present GOSstructure may be less than approximately 1.5 eV.

In some embodiments, although not shown in FIG. 2A, a second powersupply may be connected to the GOS structure. The second power supplymay be configured to cause electron emission. The second power supplymay be discussed further herein.

It is contemplated herein that one or more internal components of theillumination source 200 (e.g., the interior walls of the enclosure 202,the anode 210, the cathode 212, and like) may be configured to becleaned in accordance with ultra-high vacuum (UHV) standards usingpre-clean and pre-bake procedures. Further, it is contemplated hereinthat after assembly, the one or more internal components of theillumination source 200 (e.g., the interior walls of the enclosure 202,the anode 210, the cathode 212, and like) may be configured to beflushed with ultra-high purity (e.g., to within parts-per-trillion)argon.

In some embodiments, the broadband UV illumination source 200 mayinclude additional electrodes. For example, the broadband UVillumination source 200 may include electrode 213 to focus or direct theelectrons from cathode 212 to anode 210. In one embodiment, as depicted,electrode 213 may be at the same potential as the cathode 212. Inanother embodiment, electrode 213 may be at a more negative potentialthan cathode 212. In another embodiment, one of the cathode 212 or theanode 210 may be at ground potential.

In some embodiments, the broadband UV illumination source 200 mayinclude one or more magnets. For example, the broadband UV illuminationsource 200 may include one or more electromagnets 220. By way of anotherexample, the broadband UV illumination source 200 may include one ormore permanent magnets 221. In this embodiment, the one or more magnetsmay be configured to increase the current density as in an electronfocusing system. For example, electron trajectories tend to followspiral paths along magnetic field lines, such that the configuration ofthe one or more magnets may be adjusted to increase the electrondensity. For instance, by spacing the windings of the one or moreelectromagnets 220 more closely together near the anode 210 (rather thannear the cathode 212), the field strength will be higher near the anode,and the electron density will be increased near the anode. In theexample embodiment where the one or more electromagnets 220 are used, athird power supply 223 may be configured to apply a DC voltage to theone or more electromagnets 220 to create a static magnetic field. It isnoted herein that the broadband UV illumination source 200 may includevarious magnet configurations suitable for the focusing of the electroncurrent in the plasma. Therefore, the configuration shown in FIG. 2A isprovided merely for illustrative purposes and should not be construed aslimiting the scope of the present disclosure.

FIG. 2B illustrates a schematic diagram of a broadband ultravioletillumination source 250, in accordance with one or more alternativeembodiments of the present invention. It is noted herein that thedescription of various embodiments, components, and operations describedpreviously with respect to the characterization system 100 and broadbandillumination source 200 should be interpreted to extend to the broadbandillumination source 250 unless otherwise noted herein. As used herein,where a feature or element in FIG. 2B has the same reference label as afeature or element in FIG. 2A, it may be assumed that the feature orelement in FIG. 2B has a similar function and may be similarlyconfigured as the corresponding feature or element in FIG. 2A, unlessotherwise noted herein.

In one embodiment, the enclosure 202 of ultraviolet illumination source250 is divided into two volumes by a first anode 251. For example, anupper volume is filled with a gas 204 as described above in relation toFIG. 2A. By way of another example, a lower volume 254 contains a vacuumor a low-pressure gas, such as a gas with a pressure less than a fewPascal (Pa). The enclosure 202 and anode 251 are configured to maintaina seal between the upper and lower volumes such that the pressure in thelower volume 254 remains below a desired low pressure, such as apressure of approximately 1 Pa, over the operating life of theultraviolet illumination source 250 which may be approximately one yearor longer. Lower volume 254 contains cathode 212 which includes a GOSstructure configured to emit electrons. The emitted electrons areaccelerated toward first anode 251, which is maintained at a positivepotential relative to cathode 212 by power supply 214 a. At least aportion of anode 251 includes a thin membrane 252, such as a membranewith a thickness of less than 10 μm, that comprises a low atomic numberelement such as, but not limited to, beryllium, magnesium, aluminum, orthe like. In one embodiment, thin membrane 252 includes at least 50% byatomic composition low atomic number elements having atomic numbers of13 or lower. For example, the thin membrane 252 may include at least 50%beryllium by atomic composition. Power supply 214 a may maintain anode251 at a potential of more than +10 kV relative to cathode 212. It isnoted herein that electrons striking the thin membrane 252 may have anenergy of 10 keV or greater (corresponding to the potential differencebetween the cathode and anode) such that a significant fraction of thoseelectrons may penetrate through the thin membrane 252.

Electrons that penetrate through the thin membrane 252 into the uppervolume containing gas 204 will be accelerated towards second anode 210which is maintained at a positive potential relative to a first anode251 by power supply 214 b. Electrons travelling through gas 204 towardssecond anode 210 create plasma discharge 208 that emits broadbandradiation 216. Power supply 214 b may maintain the second anode 210 at apotential of between approximately +20 V and +200 V relative to thefirst anode 251. At least one of the power supply 214 a or the powersupply 214 b may be adjusted during operation to initiate and maintainthe plasma discharge and control the intensity of broadband emission216. Alternatively, the emission current from the cathode may beadjusted to initiate and maintain the plasma discharge. One of thecathode, the first anode, or the second anode may be at groundpotential.

In some embodiments, at least one of the lower and upper volumes mayoptionally include getters 209 a and 209 b, respectively.

FIG. 3 illustrates a cross-sectional side view diagram of a knowngraphene-dielectric-semiconductor (GOS) structure 300 suitable for useas a cathode, in accordance with one or more embodiments of the presentinvention. It is noted herein that the description of variousembodiments, components, and operations described previous with respectto the characterization system 100 should be interpreted to extend tothe GOS structure 300 unless otherwise noted herein. Further, it isnoted herein that the description of various embodiments, components,and operations described previous with respect to the broadbandillumination source 200, 250 should be interpreted to extend to the GOSstructure 300 unless otherwise noted herein.

In one embodiment, the GOS structure 300 includes a graphene-dielectricsemiconductor planar-type electron emission device. For example, the GOSstructure includes, but is not limited to, a silicon substrate 301having a top surface, a dielectric layer 302 disposed on the top surfaceof the silicon substrate 301, and at least one layer of graphene 303disposed on the top surface of the dielectric layer. In someembodiments, one or more metal contacts 304 may be formed on a topsurface of the graphene layer. It is noted herein that the GOS structure300 depicted in FIG. 3 is provided merely for illustrative purposes andshould not be construed as limiting the scope of the present disclosure.The GOS structure 300 may include any combination of layers and anyconfiguration of layers.

It is noted herein that the GOS structure 300 has several advantagessuch as low operating voltage (below 50 V), planar surface electronemission, and compatibility with standard semiconductor processes. Aspreviously noted herein, the term “graphene” refers to a single layer ofcarbon atoms arranged in a hexagonal lattice exhibiting high electricalconductivity. In addition, the electron scattering cross section ofcarbon atoms is smaller than that of conventional metal electrodes suchas gold and aluminum. Therefore, the use of graphene as the topmost gateelectrode may allow electron emission efficiency to reach 20% to 30% ifthe graphene layer is grown with low-pressure chemical vapor deposition(LPCVD).

Further, it is noted herein that the electron emission efficiency can befurther improved if only a few layers of graphene (preferably a singlegraphene layer) are used in the GOS structure 300. Owing to lowtemperature operation, unlike tungsten filaments, graphene may not be acontaminant for the broadband UV lamp and the rest of the opticalsystem. The energy spread of the present GOS structure is less thanabout 1.5 eV.

In one embodiment, the silicon substrate may be an n-type doped with adoping level. For example, the silicon substrate may be an n-type dopedwith a doping level between approximately 10¹⁶ cm⁻³ and about 10¹⁹ cm⁻³.In another embodiment, the electron emission may be, but is not requiredto be, rectangular, square, circular, or the like with linear dimensionsbetween approximately 10 μm and 1 mm. It is noted herein that electronemission 305 takes place when a bias voltage is applied across the GOSstructure 300 using second power supply 306. In preferred embodiments,the bias voltage is below 50 V. For purposes of the present disclosure,the term “emission efficiency” refers to the ratio of the emittedcurrent 305 to the current from power supply 306 through substrate 301.In a preferred embodiment, the emission efficiency increases as the biasvoltage increases and may reach 20% to 30%. It is noted herein thatalthough FIG. 3 depicts the silicon substrate as being at groundpotential, the cathode need not be grounded. As described above inrelation to FIGS. 2A and 2B, one of the cathode, the first anode, or thesecond anode may be at ground potential.

In one embodiment, the dielectric layer may be configured to be grown bythermal oxidation of silicon. In another embodiment, a dielectricmaterial other than silicon dioxide may be used. For example, thedielectric material may be boron nitride. In another embodiment, thegraphene layer(s) may be configured to be grown by low-pressure chemicalvapor deposition (LPCVD). In another embodiment, the metal contactelectrodes may be fabricated using conventional photolithography, radiofrequency sputtering, and a lift-off process. However, it is notedherein, that one or more layers of the GOS structure 300 may befabricated via any mechanism known in art, therefore the abovediscussion should not be construed as limiting the scope of the presentdisclosure.

FIG. 4 is a flow diagram depicting a method 400 for exposing a substrateto broadband UV radiation, in accordance with one or more embodiments ofthe present disclosure. It is noted herein that the steps of method 400may be implemented all or in part by system 100, 200, 250, 300. It isfurther recognized, however, that the method 400 is not limited to thesystem 100, 200, 250, 300 in that additional or alternative system-levelembodiments may carry out all or part of the steps of method 400.

In step 402, a gas is supplied to an enclosure of a broadbandillumination source. In one embodiment, the enclosure 202 of thebroadband illumination source 200 may contain a gas 204. For example,the gas 204 of the enclosure 202 may be supplied to the enclosure via anexternal gas source. For instance, the external gas source may beconfigured to supply the gas as needed to the enclosure 202. By way ofanother example, the enclosure 202 may be filled with gas 204 and thensealed. The gas may include, but is not limited to, at least one ofhydrogen, deuterium, or a noble gas such as, but not limited to, helium,neon, argon, krypton, or xenon.

In step 404, a plasma is generated inside the enclosure using a plasmadischarge device. In one embodiment, the plasma discharge device 207 isconfigured to maintain a plasma discharge 208 of the gas 204 within theenclosure 202. In another embodiment, the plasma discharge device 207includes an anode 210 positioned a select distance from a cathode 212.For example, the anode 210 and the cathode 212 may be disposed with theenclosure 202 a select distance apart.

In another embodiment, the cathode 212 includes a GOS structureincluding a graphene-dielectric-semiconductor planar-type electronemission device. For example, the GOS structure may include, but is notlimited to, a silicon substrate having a top surface, a dielectric layerdisposed on the top surface of the silicon substrate, and at least onelayer of graphene disposed on the top surface of the dielectric layer.In some embodiments, one or more metal contacts may be formed on a topsurface of the graphene layer.

In another embodiment, the GOS structure of the cathode and the anode ofthe plasma discharge device are configured to generate the plasma insidethe enclosure including the gas.

In an optional step, plasma density may be increased close to the anodeof the plasma discharge device. For example, the plasma density may beincreased close to the anode by placing one or more magnets outside theenclosure. For instance, the one or more magnets may include at leastone of a permanent magnet and an electromagnet. In an alternativeembodiment, the plasma density may be increased close to the anode byplacing one or more focusing electrodes inside the enclosure. In anotherembodiment, both focusing electrodes and magnets may be used.

In step 406, broadband ultraviolet radiation is generated. In oneembodiment, a first power supply 214 applies a DC voltage between theanode 210 and cathode 212 of the plasma discharge device. For example,the voltage may produce an electric field that maintains the discharge208. In this regard, the discharge 208 may produce broadband radiation216. In another embodiment, the first power supply 214 applies a voltagebetween the anode 210 and cathode 212 sufficient to ionize a portion ofthe gas 204 to ignite (or initiate) the discharge 208. For example, ahigh voltage (e.g., hundreds of Volts) may be applied by the first powersupply 214 to ignite the discharge and a lower voltage, (e.g., betweenapproximately 50 V and 200 V) may be applied to sustain the dischargeonce ignited. In another embodiment, the emission current may beinitially increased to initiate the discharge 208 while maintaining aconstant voltage on the anode 210.

In step 408, the broadband ultraviolet radiation is optically coupled toa substrate located outside the enclosure.

It is further contemplated that each of the embodiments of the methoddescribed above may include any other step(s) of any other method(s)described herein. In addition, each of the embodiments of the methoddescribed above may be performed by any of the systems described herein.

One skilled in the art will recognize that the herein describedcomponents, operations, devices, objects, and the discussionaccompanying them are used as examples for the sake of conceptualclarity and that various configuration modifications are contemplated.Consequently, as used herein, the specific exemplars set forth and theaccompanying discussion are intended to be representative of their moregeneral classes. In general, use of any specific exemplar is intended tobe representative of its class, and the non-inclusion of specificcomponents, operations, devices, and objects should not be taken aslimiting.

The previous description is presented to enable one of ordinary skill inthe art to make and use the invention as provided in the context of aparticular application and its requirements. As used herein, directionalterms such as “top,” “bottom,” “over,” “under,” “upper,” “upward,”“lower,” “down,” and “downward” are intended to provide relativepositions for purposes of description, and are not intended to designatean absolute frame of reference. Various modifications to the describedembodiments will be apparent to those with skill in the art, and thegeneral principles defined herein may be applied to other embodiments.Therefore, the present invention is not intended to be limited to theparticular embodiments shown and described, but is to be accorded thewidest scope consistent with the principles and novel features hereindisclosed.

With respect to the use of substantially any plural and/or singularterms herein, those having skill in the art can translate from theplural to the singular and/or from the singular to the plural as isappropriate to the context and/or application. The varioussingular/plural permutations are not expressly set forth herein for sakeof clarity.

The herein described subject matter sometimes illustrates differentcomponents contained within, or connected with, other components. It isto be understood that such depicted architectures are merely exemplary,and that in fact many other architectures can be implemented whichachieve the same functionality. In a conceptual sense, any arrangementof components to achieve the same functionality is effectively“associated” such that the desired functionality is achieved. Hence, anytwo components herein combined to achieve a particular functionality canbe seen as “associated with” each other such that the desiredfunctionality is achieved, irrespective of architectures or intermedialcomponents. Likewise, any two components so associated can also beviewed as being “connected,” or “coupled,” to each other to achieve thedesired functionality, and any two components capable of being soassociated can also be viewed as being “couplable,” to each other toachieve the desired functionality. Specific examples of couplableinclude but are not limited to physically mateable and/or physicallyinteracting components and/or wirelessly interactable and/or wirelesslyinteracting components and/or logically interacting and/or logicallyinteractable components.

Furthermore, it is to be understood that the invention is defined by theappended claims. It will be understood by those within the art that, ingeneral, terms used herein, and especially in the appended claims (e.g.,bodies of the appended claims) are generally intended as “open” terms(e.g., the term “including” should be interpreted as “including but notlimited to,” the term “having” should be interpreted as “having atleast,” the term “includes” should be interpreted as “includes but isnot limited to,” and the like). It will be further understood by thosewithin the art that if a specific number of an introduced claimrecitation is intended, such an intent will be explicitly recited in theclaim, and in the absence of such recitation no such intent is present.For example, as an aid to understanding, the following appended claimsmay contain usage of the introductory phrases “at least one” and “one ormore” to introduce claim recitations. However, the use of such phrasesshould not be construed to imply that the introduction of a claimrecitation by the indefinite articles “a” or “an” limits any particularclaim containing such introduced claim recitation to inventionscontaining only one such recitation, even when the same claim includesthe introductory phrases “one or more” or “at least one” and indefinitearticles such as “a” or “an” (e.g., “a” and/or “an” should typically beinterpreted to mean “at least one” or “one or more”); the same holdstrue for the use of definite articles used to introduce claimrecitations. In addition, even if a specific number of an introducedclaim recitation is explicitly recited, those skilled in the art willrecognize that such recitation should typically be interpreted to meanat least the recited number (e.g., the bare recitation of “tworecitations,” without other modifiers, typically means at least tworecitations, or two or more recitations). Furthermore, in thoseinstances where a convention analogous to “at least one of A, B, and C,and the like” is used, in general such a construction is intended in thesense one having skill in the art would understand the convention (e.g.,“a system having at least one of A, B, and C” would include but not belimited to systems that have A alone, B alone, C alone, A and Btogether, A and C together, B and C together, and/or A, B, and Ctogether, and the like). In those instances where a convention analogousto “at least one of A, B, or C, and the like” is used, in general such aconstruction is intended in the sense one having skill in the art wouldunderstand the convention (e.g., “a system having at least one of A, B,or C” would include but not be limited to systems that have A alone, Balone, C alone, A and B together, A and C together, B and C together,and/or A, B, and C together, and the like). It will be furtherunderstood by those within the art that virtually any disjunctive wordand/or phrase presenting two or more alternative terms, whether in thedescription, claims, or drawings, should be understood to contemplatethe possibilities of including one of the terms, either of the terms, orboth terms. For example, the phrase “A or B” will be understood toinclude the possibilities of “A” or “B” or “A and B.”

What is claimed:
 1. A broadband ultraviolet illumination source,comprising: an enclosure having one or more walls, the enclosureconfigured to contain a gas; and a plasma discharge device, the plasmadischarge device comprising: an anode; a cathode, the cathodecomprising: a silicon substrate, the silicon substrate having a topsurface; a dielectric layer, the dielectric layer disposed on the topsurface of the silicon substrate; at least one layer of graphene, the atleast one layer of graphene disposed on a top surface of the dielectriclayer; a metal contact, the metal contact formed on a top surface of thegraphene layer; and a second power supply source, the second powersource configured to apply a voltage between the metal contact and thesilicon substrate; and a first power supply source configured to apply avoltage between the anode and the cathode.
 2. The illumination source ofclaim 1, wherein at least one of the one or more walls of the enclosureis at least partly transparent at a wavelength within a range from 130nm to 400 nm.
 3. The illumination source of claim 1, wherein theenclosure includes a window, wherein the window is at least partlytransparent at a wavelength within a range from 130 nm to 400 nm.
 4. Theillumination source of claim 1, wherein the gas includes at least one ofhydrogen, deuterium, helium, neon, argon, krypton, and xenon.
 5. Theillumination source of claim 4, wherein a fill pressure of the gas isbetween 1 Pa and 10000 Pa.
 6. The illumination source of claim 4,wherein a fill pressure of the gas is between 0.1 atmospheres and 10atmospheres.
 7. The illumination source of claim 1, wherein the secondpower supply source is configured to apply a voltage between 10 V and 50V.
 8. The illumination source of claim 1, wherein the first power supplysource is configured to apply a voltage between 50 V and 200 V.
 9. Theillumination source of claim 1, further comprising one or more focusingelectrodes placed inside the enclosure.
 10. The illumination source ofclaim 1, further comprising one or more magnets placed outside theenclosure.
 11. The illumination source of claim 10, wherein the one ormore magnets comprise at least one of a permanent magnet or anelectromagnet.
 12. The illumination source of claim 1, wherein theenclosure comprises two volumes, a first volume containing the gas and asecond volume containing the cathode.